Hi,
I hate to put a sour note into an interesting thread, but if you have insurance for your modelling activities, then it could be invalid if your model fires any sort of solid projectile. This might even include the Heng Long airsofts that have a range of 2cms on a good day.
I would assume this would only apply at a display or is in a public place, so be careful! Even pyros can throw bits of cr*p quite a distance (and not always in the direction you expect - Dandare knows about exploding barrels, don't you Robert??)
I seem to remember there was a design around on the net years ago for a gun for a model based on the design of an old starting pistol. It used .22 blanks preloaded together with an airgun pellet into short bit of tube. These "cartridges" were then loaded about 7 at a time into holes in some ally bar which served as a mag. The whole mag slid one hole at a time with each shot. Interesting, but lethal and very naughty! Don't even think about it!
Personally I love anything that goes bang, whoosh or boom
Peter